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1.
Food Chem ; 337: 127745, 2021 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-32795855

RESUMO

Microalgae are a precious source of polyunsaturated fatty acids (PUFA), however extraction is difficult due to the peculiar microalgae cell structure. Here we describe a new method based on the application of chitosan nanoaggregates as CO2 responsive emulsifier, used to promote the swelling of algae cell wall and the formation of a large oil - ethanol interphase area during the ethanolysis. Tests were carried out with Pseudokirchneriella subcapitata and Nannochloropsis sp. at different biomass/ethanol/chitosan ratios. CO2 was added to trigger demulsification to promote an easy recovery of the lipid fraction. The highest yields in PUFA were obtained with Nannochloropsis sp. (207.9 mg/g of oil) using 0.4% wt of chitosan and 1:10 biomass:ethanol ratio; 43.6 mg/g of linolenic acid were obtained from Pseudokirchneriella subcapitata. Overall, because the method employs ethanol, a generally recognized as safe (GRAS) solvent, and food grade additives, it is suited for the preparation of PUFA supplements.


Assuntos
Quitosana/farmacologia , Ácidos Graxos Ômega-3/metabolismo , Microalgas/efeitos dos fármacos , Microalgas/metabolismo , Biomassa , Suplementos Nutricionais , Esterificação/efeitos dos fármacos , Etanol/farmacologia
2.
Sci Total Environ ; 752: 142168, 2021 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-33207512

RESUMO

Improving the ecological status of water sources is a growing focus for many developed and developing nations, in particular with reducing nitrogen and phosphorus in wastewater effluent. In recent years, mixotrophic micro-algae have received increased interest in implementing them as part of wastewater treatment. This is based on their ability to utilise organic and inorganic carbon, as well as inorganic nitrogen (N) and phosphorous (P) in wastewater for their growth, with the desired results of a reduction in the concentration of these substances in the water. The aim of this review is to provide a critical account of micro-algae as an important step in wastewater treatment for enhancing the reduction of N, P and the chemical oxygen demand (COD) in wastewater, whilst utilising a fraction of the energy demand of conventional biological treatment systems. Here, we begin with an overview of the various steps in the treatment process, followed by a review of the cellular and metabolic mechanisms that micro-algae use to reduce N, P and COD of wastewater with identification of when the process may potentially be most effective. We also describe the various abiotic and biotic factors influencing micro-algae wastewater treatment, together with a review of bioreactor configuration and design. Furthermore, a detailed overview is provided of the current state-of-the-art in the use of micro-algae in wastewater treatment.


Assuntos
Microalgas , Águas Residuárias , Análise da Demanda Biológica de Oxigênio , Reatores Biológicos , Nitrogênio , Fósforo , Eliminação de Resíduos Líquidos
3.
Sci Total Environ ; 752: 141747, 2021 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-32889263

RESUMO

In water environment, nitrogen (N) and phosphorus (P) are biochemically dependent nutrients following the co-limitation concept for algae growth under mixotrophic mode. From a practical viewpoint, algae growth may not bring about significant change of the background nutrient concentration of an actual waterbody in contrast to a conventional batch system. In order to better understand the growth pattern of microalgae in aquatic environments, a series of experiments were conducted under stably controlled N-P levels for studying the N-P coupling effect on mixotrophic Chlorella vulgaris growth process, with attention paid to the physiological and biochemical characteristics. It was found that within the concentration range of N = 1-8 mg·L-1 and P = 0.1-1.0 mg·L-1, the variation of the N-P level slightly affected the specific growth rate, but significantly influenced nutrients uptake, biomass dry weight, chlorophyll contents of the grown C. vulgaris. The biochemical and elemental composition of the microalgae tended to be more sensitive to the N-P concentrations and ratios in the lower nutrient range (1-2 mg N·L-1, 0.1-0.4 mg P·L-1) in which the highest N and P conversion rates were gained as 90.18 ± 1.23% and 60.47 ± 1.59%, respectively. The P assimilation and conversion efficiencies were much affected by both N and P supplies, while the P supply showed little influence on N assimilation and conversion efficiencies. It was also noticed that the N level greatly affected the metabolic pathway involving nutrient assimilation, carbohydrate fixation and monosaccharide profile, resulting in conversion of the dominant fraction of protein at N ≤ 2 mg·L-1 into other biochemical compositions including lipids at N ≥ 3 mg·L-1. The fatty acid methyl esters (FAMEs) composition tended to differ with varied nutrient levels. These findings may deepen our understanding of algal growth in aquatic environment and provide perspective for eutrophication control.


Assuntos
Chlorella vulgaris , Microalgas , Biomassa , Nitrogênio , Nutrientes , Fósforo , Águas Residuárias
4.
Sci Total Environ ; 752: 141957, 2021 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-32890823

RESUMO

This article is in the hope to open a fundamental discussion on what should future municipal wastewater treatment process be. A paradigm shift of treatment technology from present single functionality of removing to multiple-functionality of synergetic water-resource-energy recovery and carbon neutral for maximizing both environmental and economic sustainability. However, the current treatment technologies could hardly meet such requirements. It is elucidated in this article that a microalgal-bacterial granular sludge process could offer a promising option for achieving the multiple goals of municipal wastewater reclamation including energy generation, resource recovery and carbon reduction.


Assuntos
Microalgas , Águas Residuárias , Reatores Biológicos , Carbono , Esgotos , Eliminação de Resíduos Líquidos
5.
Sci Total Environ ; 752: 141708, 2021 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-32892040

RESUMO

Flocculation is a low-cost harvesting technique for microalgae biomass production, but flocculation efficiency is species dependent. In this study, we investigated the efficacy of two synthetic (polyacrylamide) and one natural (chitosan) flocculants against three algal species: the cyanobacterium Synechocystis sp., the freshwater Chlorella vulgaris, and the marine Phaeodactylum tricornutum at laboratory and pilot scales to evaluate harvesting efficiency, biomass integrity and media recycling. Growth phase affected the harvesting efficiency of the eukaryotic microalgae. The flocculation was optimal at stationary phase with high flocculation efficiency achieved using polyacrylamides at 24-36 mg/g dry weight. The effect of the flocculants on the harvested biomass was investigated. The flocculated Synechocystis sp. showed a higher proportion of compromised cells compared to C. vulgaris and P. tricornutum likely due to differences in cell walls composition. Compromised cells could lead to the release of valuable products into the surrounding growth media during flocculation. The residual culture media was recycled once with no impact on cell growth for all treatments and algal species. The flocculation technique was demonstrated at pilot-scale using 350 L microalgal suspension, showing an efficiency of 82-90% at a polyacrylamide dosage of 6.5-10 mg/L. This efficiency and the biomass quality are comparable to the laboratory-scale results. Overall, results indicate that polyacrylamide flocculants work on a wide range of species without the need for pre-treatment. The information generated in this study can contribute to making the microalgae industry more competitive.


Assuntos
Chlorella vulgaris , Microalgas , Biomassa , Floculação , Água Doce
6.
Sci Total Environ ; 751: 141599, 2021 Jan 10.
Artigo em Inglês | MEDLINE | ID: mdl-32890799

RESUMO

Treatment of industrial and domestic wastewater is very important to protect downstream users from health risks and meet the freshwater demand of the ever-increasing world population. Different types of wastewater (textile, dairy, pharmaceutical, swine, municipal, etc.) vary in composition and require different treatment strategies. Wastewater management and treatment is an expensive process; hence, it is important to integrate relevant technology into this process to make it more feasible and cost-effective. Wastewater treatment using microalgae-based technology could be a global solution for resource recovery from wastewater and to provide affordable feedstock for bioenergy (biodiesel, biohydrogen, bio-alcohol, methane, and bioelectricity) production. Various microalgal cultivation systems (open or closed photobioreactors), turf scrubber, and hybrid systems have been developed. Although many algal biomass harvesting methods (physical, chemical, biological, and electromagnetic) have been reported, it is still an expensive process. In this review article, resource recovery from wastewater using algal cultivation, biomass harvesting, and various technologies applied in converting algal biomass into bioenergy, along with the various challenges that are encountered are discussed in brief.


Assuntos
Microalgas , Animais , Biocombustíveis , Biomassa , Fotobiorreatores , Suínos , Águas Residuárias
7.
J Environ Sci (China) ; 99: 175-186, 2021 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-33183695

RESUMO

Microalgae and cyanobacteria are fundamental components of aquatic ecosystems. Pollution in aquatic environment is a worldwide problem. Toxicological research on microalgae and cyanobacteria can help to establish a solid foundation for aquatic ecotoxicological assessments. Algae and cyanobacteria occupy a large proportion of the biomass in aquatic environments; thus, their toxicological responses have been investigated extensively. However, the depth of toxic mechanisms and breadth of toxicological investigations need to be improved. While existing pollutants are being discharged into the environment daily, new ones are also being produced continuously. As a result, the phenomenon of water pollution has become unprecedentedly complex. In this review, we summarize the latest findings on five kinds of aquatic pollutants, namely, metals, nanomaterials, pesticides, pharmaceutical and personal care products (PPCPs), and persistent organic pollutants (POPs). Further, we present information on emerging pollutants such as graphene, microplastics, and ionic liquids. Efforts in studying the toxicological effects of pollutants on microalgae and cyanobacteria must be increased in order to better predict the potential risks posed by these materials to aquatic ecosystems as well as human health.


Assuntos
Cianobactérias , Poluentes Ambientais , Microalgas , Poluentes Químicos da Água , Ecossistema , Humanos , Plásticos , Poluentes Químicos da Água/toxicidade
8.
Chemosphere ; 262: 127881, 2021 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-32795709

RESUMO

The recovery of microalgae by means of coagulation-flocculation is efficient, simple and low operating costs. The addition of coagulants makes it possible to destabilize the microalgae surface loads and recover their biomass. Chemical coagulants can contaminate the environment and negatively affect human health. Thus, the exploration of natural coagulants, such as Moringa oleifera and Guazuma ulmifolia, are innovative. Thus, this study aimed to evaluate the efficiency of biomass separation from the microalgae Scenedesmus obliquuos by means of coagulation-flocculation. M. oleifera and G. ulmifolia were used in order to optimize the variables dose, pH and settling time, through a central composite rotational design, which presented recovery efficiencies above 80.0% and 60.0%, respectively. In relation to M. oleifera, optimum regions were obtained for biomass recovery at both pH 4.0 with a dose of 40.0 mg L-1 and pH 9.0 with a dose of 80.0 mg L-1, both in 30 min of settling times. For G. ulmifolia, an optimum dose of 30.0 mg L-1 at pH 4.0 with a 3 min settling time demonstrated that this new coagulant for microalgae recovery has potential for application. Thus, these natural coagulants are promising and can be used in coagulation-flocculation to recover biomass from Scenedesmus obliquuos and, thus, minimize the use of synthetic or metallic products.


Assuntos
Scenedesmus/fisiologia , Biomassa , Floculação , Humanos , Microalgas , Moringa oleifera
9.
Chemosphere ; 262: 128422, 2021 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-33182085

RESUMO

This study evaluated the toxicity of Cr(VI) to microalgae Chlorella vulgaris, and its removal by continuous microalgae cultivation in membrane photobioreactor (MPBR). Batch cultivation in photobioreactors showed that low concentration of Cr(VI) (0.5 and 1.0 mg L-1) stimulated the growth of C. vulgaris, while 2.0 and 5.0 mg L-1 Cr(VI) in the wastewater significantly inhibited the growth of C. vulgaris. Superoxide dismutase and catalase activities that represented cellular antioxidant capacity significantly increased at 0.5 and 1.0 mg L-1 Cr(VI), and then gradually decreased with the continuous increase of Cr(VI) concentration. The content of malondialdehyde, which represents the degree of cellular oxidative damage, increased with the increase of Cr(VI) concentration and reached the peak value at 2.0 mg L-1 Cr(VI). C. vulgaris was then cultured in MPBR equipped with hollow-fiber ultrafiltration membrane module to achieve continuous removal of Cr from wastewater. With the in-situ solid-liquid separation function of the membrane module, solid retention time (SRT) and hydraulic retention time (HRT) of the reactor could be controlled separately. Experimental results showed that both SRT and HRT had significant effects on the algal biomass production and pollutants removal. During the continuous operation, MPBR achieved a maximum total Cr reduction of 50.0% at HRT of 3-day and SRT of 40-day, and a maximum volumetric removal rate of total Cr of 0.21 mg L-1 d-1 at HRT of 2-day and SRT of 40-day.


Assuntos
Chlorella vulgaris/fisiologia , Cromo/toxicidade , Fotobiorreatores , Eliminação de Resíduos Líquidos , Biomassa , Chlorella vulgaris/crescimento & desenvolvimento , Cromo/análise , Estudos Longitudinais , Membranas Artificiais , Microalgas/crescimento & desenvolvimento , Oxirredução , Águas Residuárias
10.
Chemosphere ; 262: 127939, 2021 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-33182115

RESUMO

Species specific nitrogen-to-phosphorus molar ratio (NPR) has been suggested for green microalgae. Algae can store nitrogen and phosphorus, suggesting that the optimum feed concentration dynamically changes as function of the nutrient storage. We assessed the effect of varying influent NPR on microalgal cultivation in terms of microbial community stability, effluent quality and biokinetics. Mixed green microalgae (Chlorella sorokiniana and Scenedesmus sp.) and a monoculture of Chlorella sp. were cultivated in continuous laboratory-scale reactors treating used water. An innovative image analysis tool, developed in this study, was used to track microbial community changes. Diatoms proliferated as influent NPR decreased, and were outcompeted once cultivation conditions were restored to the optimal NPR range. Low NPR operation resulted in decrease in phosphorus removal, biomass concentration and effluent nitrogen concentration. ASM-A kinetic model simulation results agreed well with operational data in the absence of diatoms. The failure to predict operational data in the presence of diatoms suggest differences in microbial activity that can significantly influence nutrient recovery in photobioreactors (PBR). No contamination occurred during Chlorella sp. monoculture cultivation with varying NPRs. Low NPR operation resulted in decrease in biomass concentration, effluent nitrogen concentration and nitrogen quota. The ASM-A model was calibrated for the monoculture and the simulations could predict the experimental data in continuous operation using a single parameter subset, suggesting stable biokinetics under the different NPR conditions. Results show that controlling the influent NPR is effective to maintain the algal community composition in PBR, thereby ensuring effective nutrients uptake.


Assuntos
Microalgas/fisiologia , Nitrogênio/análise , Fósforo/análise , Purificação da Água/métodos , Biomassa , Chlorella , Nutrientes , Fotobiorreatores , Scenedesmus , Águas Residuárias , Água
11.
An Acad Bras Cienc ; 92(suppl 2): e20190050, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-33174910

RESUMO

The aim of this study was to evaluate the effect of phosphorus (P) on the toxicity of zinc (Zn) for the alga Raphidocelis subcapitata. P was provided in three concentrations: 2.3 x 10-4 mol L-1, 2.3 x 10-6 mol L-1 and 1.0 x 10-6 mol L-1. Algal cells were acclimated to the specific P concentrations before the start of the experiment. The chemical equilibrium software MINEQL+ 4.61 was employed to calculate the Zn2+ concentration. After acclimated, the algal cells were inoculated into media containing different Zn concentrations (0.09 x 10-6 mol L-1 to 9.08 x 10-6 mol L-1). The study showed that besides the reduction in algal growth rates, phosphorus had an important influence on the toxicity of zinc for microalga. The inhibitory Zn2+ concentration values for R. subcapitata were 2.74 x 10-6 mol L-1, 0.58 x 10-6 mol L-1 and 0.24 x 10-6 mol L-1 for the microalgae acclimated at P concentrations of 2.3 x 10-4 mol L-1, 2.3 x 10-6 mol L-1 and 1.0 x 10-6 mol L-1, respectively. Ecotoxicological studies should consider the interaction between metal concentrations and varying P values to provide realistic data of what occurs in phytoplankton communities in environments.


Assuntos
Clorófitas , Microalgas , Poluentes Químicos da Água , Zinco , Fósforo/farmacologia , Poluentes Químicos da Água/análise , Poluentes Químicos da Água/toxicidade , Zinco/toxicidade
12.
Bioresour Technol ; 318: 124266, 2020 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-33099096

RESUMO

Anaerobic fermentation of microalgae was always hindered by its rigid cell wall structure. This paper reports a novel technique, i.e., adding potassium ferrate (K2FeO4) into microalgae fermentation systems to enhance short-chain fatty acids (SCFAs) production. The results showed that the maximum SCFAs production and acetic acid proportion were 732.6 mg COD/g VS and 54.6% at a dosage of 112.8 mg Fe(VI)/g VS, which were 168% and 208% of those in the control, respectively. Mechanism studies revealed that K2FeO4 effectively destroyed surface morphology and cell structure, and thus facilitated microalgae solubilization, providing a large number of biodegradable substrates for subsequent SCFA production. Although K2FeO4 inhibited all the microbial activities relevant to hydrolysis, acidification and methanogenesis processes to some degree, its inhibition to methanogens was much severer than that to other microbes. Illumina MiSeq sequencing analyses revealed that K2FeO4 addition increased the relative abundance (from 9.45% to 50.4%) of hydrolytic and SCFAs-forming bacteria.


Assuntos
Microalgas , Ácidos Graxos Voláteis , Estudos de Viabilidade , Fermentação , Compostos de Ferro , Compostos de Potássio , Esgotos
13.
Bioresour Technol ; 318: 124253, 2020 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-33129070

RESUMO

Microalgal biohydrogen (bioH2) has attracted global interest owing to its potential carbon-free source of sustainable renewable energy. Most of previous reviews which focused on microalgal bioH2, have shown unclear differentiation among the metabolic pathways. In this review, investigation of all different metabolic pathways for microalgal bioH2 production along with discussion on the recent research work of last 5-years have been considered. The major factors (such as light, vital nutrients, microalgal cell density, and substrate bioavailability) are highlighted. Moreover, effect of various pretreatment approaches on the constituent's bioaccessibility is reported. Microbial electrolysis cells as a new strategy for bioH2 production is stated. Comparison between the operation conditions of various bioreactors and economic feasibility is also emphasized. Genetic, metabolic engineering, and synthetic biology as recent technologies improved the microalgal bioH2 production through inactivation of uptake hydrogenase (H2ase), inhibition of the competing pathways in polysaccharide synthesis, and improving the O2 tolerant H2ase.


Assuntos
Microalgas , Biocombustíveis , Reatores Biológicos , Fermentação , Hidrogênio/análise , Redes e Vias Metabólicas
14.
Chemosphere ; 261: 128199, 2020 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-33113666

RESUMO

A microalgal-bacterial membrane photobioreactor (MB-MPBR) was developed for simultaneous COD and nutrients (N and P) removals from synthetic municipal wastewater in a single stage for a long-term operation over 350 days. The effects of hydraulic retention time (HRT) and N/P ratio on the biological performance were systematically evaluated for the first time. The results showed that a lower N/P ratio (3.9:1) and shorter HRT (2 d) promoted more biomass production, as compared to a high HRT (3 d) and a high N/P ratio (9.7:1). The highest biomass concentration (2.55 ± 0.14 g L-1) and productivity (127.5 mg L-1·d-1) were achieved at N/P ratio of 3.9:1 and HRT of 2 d due to the highest nitrogen and phosphorus loadings under such conditions. A COD and ammonia-N removal efficiency of over 96% and 99%, respectively, were achieved regardless of HRTs and N/P ratios. In the absence of nitrogen or phosphorus deficiency, shorter HRT (2 d) yielded a higher nitrogen and phosphorus uptake but lower removal efficiency. In addition, the imbalance N/P ratio (9.7:1) would decrease nitrogen or phosphorus removal. Overall, the results suggested that it was feasible to simultaneously achieve complete or high removal of COD, nitrogen, and phosphorous in MB-MPBR under the appropriate conditions. This study demonstrated for the first time that MB-MPBR is a promising technology that could achieve a high-quality effluent meeting the discharge standards of COD and nutrients in one single step.


Assuntos
Nitrogênio/metabolismo , Fósforo/metabolismo , Fotobiorreatores , Eliminação de Resíduos Líquidos/instrumentação , Amônia/metabolismo , Análise da Demanda Biológica de Oxigênio , Biomassa , Chlorella vulgaris/metabolismo , Microalgas/metabolismo , Nitrogênio/análise , Fotobiorreatores/microbiologia , Eliminação de Resíduos Líquidos/métodos , Águas Residuárias/química
15.
Sci Total Environ ; 748: 142464, 2020 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-33113682

RESUMO

Nannochloropsis sp. has received increased attention by researchers in recent years due to its complexity and abundance of lipid structures. The lipids of this microalgae species have been identified to contain large quantities of neutral lipids which are capable of producing raw materials for nutraceuticals, food additives and biofuels. The production of biodiesel has received the greatest attention as there is an increase in global demand for both more fuel and more environmentally sustainable methods to produce such resources. The greatest challenges facing industries to mass produce viable products from microalgae involve the degradation of the cell wall and extracting the fatty acid of interest due to high costs. Various studies have shown that the extraction lipids from the microalgae can greatly influence the overall fatty acid composition. Different extraction methods can result in recovering higher quantities of either saturated fatty acids, monounsaturated fatty acids or polyunsaturated fatty acids. Biodiesel production requires higher quantities of saturated fatty acids and monosaturated fatty acids as increased quantities of polyunsaturated fatty acids result in oxidation which decreases the performance of the biodiesel. Whereas, polyunsaturated fatty acids are required in order to produce pharmaceuticals and food additives such as omega 3. This review will focus on how different in-situ extraction methods for lipid and fatty acid recovery, influence the fatty acid composition of various Nannochloropsis species (oculate, gaditana, salina and oceanica). The mechanical methods (microwave, ultrasonic and supercritical­carbon dioxide) of extraction for Nannochloropsis sp. will be critically evaluated. The use of enzymes will also be addressed, for their ability to extract fatty acids in a more environmentally friendly manner. This paper will report on the viable by-products which can be produced using different extraction methods.


Assuntos
Microalgas , Estramenópilas , Biocombustíveis , Biomassa , Ácidos Graxos , Lipídeos
16.
Sci Total Environ ; 748: 142383, 2020 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-33113702

RESUMO

Hydrothermal carbonization (HTC)/liquefaction (HTL)/gasification (HTG) are promising processes for biofuel production from biomass containing high moisture. However, wastewater, the aqueous phase (AP) byproduct from these hydrothermal processes, is inevitably produced in large amounts. The AP contains >20% of the biomass carbon, and the total organic carbon in AP is as high as 10-20 g/L. The treatment and utilization of AP are becoming a bottleneck for the industrialization of hydrothermal technologies. The major challenges are the presence of various inhibitory substances and the high complexity of AP. Bioenergy recovery from AP has attracted increasing interest. In the present review, the compositions and characteristics of AP are first presented. Then, the progress in recovering bioenergy from AP by recirculation as the reaction solvent, anaerobic digestion (AD), supercritical water gasification (SCWG), microbial fuel cell (MFC), microbial electrolysis cell (MEC), and microalgae cultivation is discussed. Recirculation of AP as reaction solvent is preferable for AP from biomass with relatively low moisture; AD, MFC/MEC, and microalgae cultivation are desirable for the treatment of AP produced from processing biomass with low lignin content at relatively low temperatures; SCWG is widely applicable but is energy-intensive. Finally, challenges and corresponding strategies are proposed to promote the development of AP valorization technologies. Comprehensive analysis of AP compositions, clarification of the mechanisms of valorization processes, valorization process integration detoxification of AP, polycultures and co-processing of AP with other waste, enhancement in pollutant removal, scaling-up performance, and the techno-economic analysis and life-cycle assessment of valorization systems are promising directions in future investigations.


Assuntos
Microalgas , Águas Residuárias , Biocombustíveis , Biomassa , Temperatura
17.
Water Sci Technol ; 82(5): 851-860, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-33031065

RESUMO

The microalgae treatment system is an economically and environmentally friendly option for wastewater treatment. However, the effects of heavy metal toxicity on microalgae cells can limit the use of microalgae in the treatment of industrial effluents rich in heavy metals. In this work, we studied the effect of Ni, Cu, Al, Hg and Pb, added as single-metal solutions to the microalgae culture medium, on the growth of 20 indigenous strains belonging to a wide variety of microalgae genera. Ni and Cu were the most toxic to the strains tested. A highly tolerant strain of the Phacus genera was selected. We determined the effect of multiple combinations of Ni, Al and Pb on the cell growth of the selected strain and on the removal capacity of each metal from the microalgae culture medium. Phacus was able to grow in the multi-metal solution (Ni, 5.00 mg/L; Al, 9.94 mg/L and Pb 1.00 mg/L) and to efficiently remove the metals, with removal capacities of 8.82 ±0.16 mg/g for Ni, 2.09 ± 0.05 mg/g for Pb and 16.90 ± 0.53 mg/g for Al. The reductions of Ni, Al and Pb concentrations were 66.67, 64.28 and 79.17% respectively.


Assuntos
Metais Pesados , Microalgas , Biodegradação Ambiental , Chumbo/toxicidade , Metais Pesados/análise , Metais Pesados/toxicidade , Águas Residuárias
18.
Water Sci Technol ; 82(6): 1009-1024, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-33055392

RESUMO

In microalgae harvesting, flocculation is usually a compulsory preliminary step to further separation by sedimentation or flotation. For some microalgae species, and under certain growth conditions, flocculation can occur naturally. Natural flocculation presents many advantages as it does not require the addition of any flocculants to the culture medium and shows high efficiency rate. But because natural flocculation is so specific to the species and conditions, and thanks to the knowledge accumulated over the last years on flocculation mechanisms, researchers have developed strategies to induce this natural harvesting. In this review, we first decipher at the molecular scale the underlying mechanisms of natural flocculation and illustrate them by selected studies from the literature. Then we describe the developed strategies to induce natural flocculation that include the use of biopolymers, chemically modified or not, or involve mixed species cultures. But all these strategies need the addition of external compounds or microorganism which can present some issues. Thus alternative directions to completely eliminate the need for an external molecule, through genetic engineering of microalgae strains, are presented and discussed in the third part of this review.


Assuntos
Microalgas , Bioensaio , Biomassa , Meios de Cultura , Floculação
19.
Water Sci Technol ; 82(6): 1025-1030, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-33055393

RESUMO

Microalgae can synthesise the ozone depleting pollutant and greenhouse gas nitrous oxide (N2O). Consequently, significant N2O emissions have been recorded during real wastewater treatment in high rate algal ponds (HRAPs). While data scarcity and variability prevent meaningful assessment, the magnitude reported (0.13-0.57% of the influent nitrogen load) is within the range reported by the Intergovernmental Panel on Climate Change (IPCC) for direct N2O emissions during centralised aerobic wastewater treatment (0.016-4.5% of the influent nitrogen load). Critically, the ability of microalgae to synthesise N2O challenges the IPCC's broad view that bacterial denitrification and nitrification are the only major cause of N2O emissions from wastewater plants and aquatic environments receiving nitrogen from wastewater effluents. Significant N2O emissions have indeed been repeatedly detected from eutrophic water bodies and wastewater discharge contributes to eutrophication via the release of nitrogen and phosphorus. Considering the complex interplays between nitrogen and phosphorus supply, microalgal growth, and microalgal N2O synthesis, further research must urgently seek to better quantify N2O emissions from microalgae-based wastewater systems and eutrophic ecosystems receiving wastewater. This future research will ultimately improve the prediction of N2O emissions from wastewater treatment in national inventories and may therefore affect the prioritisation of mitigation strategies.


Assuntos
Gases de Efeito Estufa , Microalgas , Ecossistema , Óxido Nitroso/análise , Águas Residuárias/análise
20.
Water Sci Technol ; 82(6): 1044-1061, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-33055395

RESUMO

This study evaluates the feasibility of advanced biofilm microalgae cultivation in a twin layer (TL) system for nutrient removal (N and P) as the tertiary treatment in small wastewater treatment plants (WWTPs) located in sensitive areas. Furthermore, the potential valorisation of microalgae biomass as a component of bio-based fertilizers is assessed. Scenedesmus sp. was chosen among 33 microalgae strains for inoculation of TL due to its high growth rate and its nutrient uptake capacity. The tests carried out in the prototype were markedly efficient for total soluble and ammoniacal nitrogen removal (up to 66 and 94%, respectively). In terms of potential valorisation of microalgae, the nutrient content was 5.5% N (over 40% protein), 8.8% P2O5 and 1.5% K2O, high enzymatic activity, very low levels of heavy metals and no detectable pathogen presence. However, in the formulation of solid-state bio-based fertilizers, the microalgae proportions in blends of over 2% of microalgae led to negative effects on ryegrass (Lolium perenne L. ssp.) and barley (Hordeum vulgare ssp.). The obtained results demonstrate that TL represents a promising technology, which allows efficient tertiary treatment of urban wastewater and the production of high-quality bio-based fertilizer.


Assuntos
Microalgas , Scenedesmus , Biomassa , Nutrientes , Águas Residuárias
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